Linear drives of the type described above include an electromotor that provides the rotational drive movement, for example, or a drive wheel or pulley, and a runner that is secured to a flexible member running around a guide member such as a guide pulley. The electric motor runs in one direction for moving the runner one linear direction and the rotational direction of the electric motor is reversed for moving the runner in the opposite direction.
It is also known to drive a spindle by means of an electromotor. The runner has a female threading that engages the threading of the spindle, whereby the runner can be positioned anywhere along the length of the spindle. In known linear drives, the electric motor is frequently arranged in the area of one end of the linear drive, whereby such an arrangement in combination with the available installation space for a given installation length of the linear drive, reduces the available stroke range of the linear movement of the runner. Another disadvantage of conventional drives this type is seen in that the electromotor frequently extends substantially to the side of the longitudinally movable runner so that depending on the arrangement of the motor a substantial installation space is required in the direction of the longitudinal movement of the runner or in the direction across the movement direction, or even in both directions. Such an installation space or volume does not pose a substantial problem on the ground in the workshop or assembly sheds. However, when such drives are to be used in air or spacecraft, the available installation volume is very limited, whereby the installation of such Linear drives poses substantial difficulties. As a result, heretofore such linear drives have been used on a rather limited scale in air and spacecraft.
German Patent Publication (DE) 3,836,372 A1 (Holtkamp) published May 3, 1990 discloses an apparatus for converting the rotational movement of a spindle into a longitudinal movement of a runner or trip dog, whereby the spindle is constructed as a flexible endless tension spindle having an external threading. The spindle passes through a hollow shaft that is rotated by an electric motor and which is fixed against axial displacement. The hollow snarl is equipped with a drive ball that engages into the threading of the spindle. Thus, when the hollow shaft rotates, the spindle travels axially through the motor. This conventional construction requires that one half of the motor diameter is located on each side of the longitudinal spindle axis. Additionally, there must be space outside the motor for the return path of the flexible spindle. Thus, a compact construction is possible only within limits.